56 lines
1.4 KiB
Python
56 lines
1.4 KiB
Python
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#!/usr/bin/env python
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import itertools
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import sys
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from typing import List, Tuple
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def solve(circle: List[int]) -> int:
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def to_links(circle: List[int]) -> List[int]:
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links = [-1 for __ in range(len(circle) + 1)]
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cyclic = itertools.cycle(circle)
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next(cyclic) # Advance it by one
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for prev, cur in zip(circle, cyclic):
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links[prev] = cur
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return links
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def step(links: List[int], current: int) -> int:
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cup0 = links[current]
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cup1 = links[cup0]
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cup2 = links[cup1]
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links[current] = links[cup2] # Remove 3-tuple from the linked-list
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# Find destination
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dest = (current - 1) if current > 1 else (len(links) - 1)
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while dest in (cup0, cup1, cup2):
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dest = (dest - 1) if dest > 1 else (len(links) - 1)
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# Update our links
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links[cup2], links[dest] = links[dest], cup0
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return links[current] # What's the next value in the cycle ?
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def to_answer(links: List[int]) -> int:
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next = links[1]
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return next * links[next]
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current = circle[0]
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circle += [i + 1 for i in range(max(circle), 1000000)]
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links = to_links(circle)
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for __ in range(10000000):
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current = step(links, current)
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return to_answer(links)
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def main() -> None:
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input = [line.strip() for line in sys.stdin.readlines()]
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assert len(input) == 1
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print(solve([int(c) for c in input[0]]))
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if __name__ == "__main__":
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main()
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